Brenno Caetano Troca Cabella

Non-extensive entropy and the extraction of BOLD spatial information in event-related functional MRI.

Functional magnetic resonance imaging (fMRI) data analysis has been carried out recently in the framework of information theory, by means of the Shannon entropy. As a natural extension, a method based on the generalized Tsallis entropy was developed to the analysis event-related (ER-fMRI), where a brief stimulus is presented, followed by a long period of rest. The new technique aims for spatial localization neuronal activity due to a specific task. This method does not require a priori hypothesis of the hemodynamic response function (HRF) shape and the linear relation between BOLD responses with the presented task. Numerical simulations were performed so as to determine the optimal values of the Tsallis q parameter and the number of levels, L. In order to avoid undesirable divergences of the Tsallis entropy, only positive q values were studied. Results from simulated data (with L = 3) indicated that, for q = 0.8, the active brain areas are detected with the highest performance. Moreover, the method was tested for an in vivo experiment and demonstrated the ability to discriminate active brain regions that selectively responded to a bilateral motor task.

Data collapse, scaling functions, and analytical solutions of generalized growth models.

We consider several one-species population dynamics model with finite and infinite carrying capacity, time dependent growth and effort rates and solve them analytically. We show that defining suitable scaling functions for a given time, one is able to demonstrate that their ratio with respect to its initial value is universal. This ratio is independent from the initial condition and from the model parameters. Although the effort rate does not break the model universality it produces a transition between the species extinction and survival. A general formula is furnished to obtain the scaling functions.

Effective carrying capacity and analytical solution of a particular case of the Richards-like two-species population dynamics model

We consider a generalized two-species population dynamic model and analytically solve it for the amensalism and commensalism ecological interactions. These two-species models can be simplified to a one-species model with a time dependent extrinsic growth factor. With a one-species model with an effective carrying capacity one is able to retrieve the steady state solutions of the previous one-species model. The equivalence obtained between the effective carrying capacity and the extrinsic growth factor is complete only for a particular case, the Gompertz model. Here we unveil important aspects of sigmoid growth curves, which are relevant to growth processes and population dynamics.

An agent-based computational model of the spread of tuberculosis

In this work we propose an alternative model of the spread of tuberculosis (TB) and the emergence of drug resistance due to the treatment with antibiotics. We implement the simulations by an agent-based model computational approach where the spatial structure is taken into account. The spread of tuberculosis occurs according to probabilities defined by the interactions among individuals. The model was validated by reproducing results already known from the literature in which different treatment regimes yield the emergence of drug resistance. The different patterns of TB spread can be visualized at any time of the system evolution. The implementation details as well as some results of this alternative approach are discussed.

Associations Between Impaired Cerebral Blood Flow Autoregulation, Cerebral Oxygenation, and Biomarkers of Brain Injury and Postoperative Cognitive Dysfunction in Elderly Patients After Major Noncardiac Surgery

BACKGROUND: Increasing evidence links postoperative cognitive dysfunction (POCD) to surgery and anesthesia. POCD is recognized as an important neuropsychological adverse outcome in surgical patients, particularly the elderly. This prospective cohort study aimed to investigate whether POCD is associated with impaired intraoperative cerebral autoregulation and oxygenation, and increased levels of biomarkers of brain injury. METHODS: Study subjects were patients ≥65 years of age scheduled for major noncardiac surgery. Cognitive function was assessed before and 1 week after surgery. POCD was diagnosed if a decline of >1 standard deviation of z-scores was present in ≥2 variables of the test battery. The incidence of POCD 1 week after surgery was modeled as a multivariable function of the index of autoregulation (MxA) and tissue oxygenation index (TOI), adjusting for baseline neuropsychological assessment battery (Consortium to Establish a Registry for Alzheimer’s Disease-Neuropsychological Assessment Battery [CERAD-NAB]) total score and the maximum C-reactive protein (CRP) concentration. The biomarkers of brain injury neuron-specific enolase and S100&bgr; protein, age, and level of education were included in secondary multivariable logistic regression analyses. RESULTS: Of the 82 patients who completed the study, 38 (46%) presented with POCD 1 week after surgery. In the multivariable regression analysis, higher intraoperative MxA (odds ratio [OR; 95% confidence interval (CI)], 1.39 [1.01–1.90] for an increase of 0.1 units, P = .08 after Bonferroni adjustment), signifying less effective autoregulation, was not associated with higher odds of POCD. The univariable logistic regression model for MxA yielded an association with POCD (OR [95% CI], 1.44 [1.06–1.95], P = .020). Tissue oxygenation index (1.12 [0.41–3.01] for an increase of 10%, P = 1.0 after Bonferroni adjustment) and baseline CERAD-NAB total score (0.80 [0.45–1.42] for an increase of 10 points, P = .45) did not affect the odds of POCD. POCD was associated with elevated CRP on postoperative day 2 (median [interquartile range]; 175 [81–294] vs 112 [62–142] mg/L, P = .033); however, the maximum CRP value (OR [95% CI], 1.35 [0.97–1.87] for a 2-fold increase, P = .07) had no distinct effect on POCD. CONCLUSIONS: Impairment of intraoperative cerebral blood flow autoregulation is not predictive of early POCD in elderly patients, although secondary analyses indicate that an association probably exists.

Prospective study on non-invasive assessment of ICP in head injured patients: comparison of four methods

DC is supported by a Cambridge Commonwealth, European & International Trust Scholarship, University of Cambridge. JD is supported by a Woolf Fisher Trust Scholarship. XL is supported by a Gates Cambridge Scholarship. GVV is supported by an A. G. Leventis Foundation Scholarship, and a Charter Studentship from St Edmund’s College, Cambridge. SM and GF are supported by the Pan-American Health Organization. DC and MC are partially supported by NIHR Brain Injury Healthcare Technology Co-operative, Cambridge, UK.

Generalized Allee effect model.

The Allee effect consists of a positive correlation between very small population size and fitness. Offering a new view point on the weak and strong demographic Allee effect, we propose to combine them with the Richards growth model. In particular, a peculiar manifestation of the Allee effect is analytically predicted and still not validated by experiments. Model validation with ecological data is presented for some special situations.

Richards-like two species population dynamics model

The two-species population dynamics model is the simplest paradigm of inter- and intra-species interaction. Here, we present a generalized Lotka–Volterra model with intraspecific competition, which retrieves as particular cases, some well-known models. The generalization parameter is related to the species habitat dimensionality and their interaction range. Contrary to standard models, the species coupling parameters are general, not restricted to non-negative values. Therefore, they may represent different ecological regimes, which are derived from the asymptotic solution stability analysis and are represented in a phase diagram. In this diagram, we have identified a forbidden region in the mutualism regime, and a survival/extinction transition with dependence on initial conditions for the competition regime. Also, we shed light on two types of predation and competition: weak, if there are species coexistence, or strong, if at least one species is extinguished.

Individualizing Thresholds of Cerebral Perfusion Pressure Using Estimated Limits of Autoregulation

Objectives: In severe traumatic brain injury, cerebral perfusion pressure management based on cerebrovascular pressure reactivity index has the potential to provide a personalized treatment target to improve patient outcomes. So far, the methods have focused on identifying “one” autoregulation-guided cerebral perfusion pressure target—called “cerebral perfusion pressure optimal”. We investigated whether a cerebral perfusion pressure autoregulation range—which uses a continuous estimation of the “lower” and “upper” cerebral perfusion pressure limits of cerebrovascular pressure autoregulation (assessed with pressure reactivity index)—has prognostic value. Design: Single-center retrospective analysis of prospectively collected data. Setting: The neurocritical care unit at a tertiary academic medical center. Patients: Data from 729 severe traumatic brain injury patients admitted between 1996 and 2016 were used. Treatment was guided by controlling intracranial pressure and cerebral perfusion pressure according to a local protocol. Interventions: None. Methods and Main Results: Cerebral perfusion pressure-pressure reactivity index curves were fitted automatically using a previously published curve-fitting heuristic from the relationship between pressure reactivity index and cerebral perfusion pressure. The cerebral perfusion pressure values at which this “U-shaped curve” crossed the fixed threshold from intact to impaired pressure reactivity (pressure reactivity index = 0.3) were denoted automatically the “lower” and “upper” cerebral perfusion pressure limits of reactivity, respectively. The percentage of time with cerebral perfusion pressure below (%cerebral perfusion pressure < lower limit of reactivity), above (%cerebral perfusion pressure > upper limit of reactivity), or within these reactivity limits (%cerebral perfusion pressure within limits of reactivity) was calculated for each patient and compared across dichotomized Glasgow Outcome Scores. After adjusting for age, initial Glasgow Coma Scale, and mean intracranial pressure, percentage of time with cerebral perfusion pressure less than lower limit of reactivity was associated with unfavorable outcome (odds ratio %cerebral perfusion pressure < lower limit of reactivity, 1.04; 95% CI, 1.02–1.06; p < 0.001) and mortality (odds ratio, 1.06; 95% CI, 1.04–1.08; p < 0.001). Conclusions: Individualized autoregulation-guided cerebral perfusion pressure management may be a plausible alternative to fixed cerebral perfusion pressure threshold management in severe traumatic brain injury patients. Prospective randomized research will help define which autoregulation-guided method is beneficial, safe, and most practical.

Assessment of non-invasive ICP during CSF infusion test: an approach with transcranial Doppler

BackgroundThis study aimed to compare four non-invasive intracranial pressure (nICP) methods in a prospective cohort of hydrocephalus patients whose cerebrospinal fluid dynamics was investigated using infusion tests involving controllable test-rise of ICP.MethodCerebral blood flow velocity (FV), ICP and non-invasive arterial blood pressure (ABP) were recorded in 53 patients diagnosed for hydrocephalus. Non-invasive ICP methods were based on: (1) interaction between FV and ABP using black-box model (nICP_BB); (2) diastolic FV (nICP_FVd); (3) critical closing pressure (nICP_CrCP); (4) transcranial Doppler-derived pulsatility index (nICP_PI). Correlation between rise in ICP (∆ICP) and ∆nICP and averaged correlations for changes in time between ICP and nICP during infusion test were investigated.ResultsFrom baseline to plateau, all nICP estimators increased significantly. Correlations between ∆ICP and ∆nICP were better represented by nICP_PI and nICP_BB: 0.45 and 0.30 (p < 0.05). nICP_FVd and nICP_CrCP presented non-significant correlations: −0.17 (p = 0.21), 0.21 (p = 0.13). For changes in ICP during individual infusion test nICP_PI, nICP_BB and nICP_FVd presented similar correlations with ICP: 0.39 ± 0.40, 0.39 ± 0.43 and 0.35 ± 0.41 respectively. However, nICP_CrCP presented a weaker correlation (R = 0.29 ± 0.24).ConclusionsOut of the four methods, nICP_PI was the one with best performance for predicting changes in ∆ICP during infusion test, followed by nICP_BB. Unreliable correlations were shown by nICP_FVd and nICP_CrCP. Changes of ICP observed during the test were expressed by nICP values with only moderate correlations.